1. Field of the Invention
The present invention relates to a valve for ball. Further, the present invention relates to a method of manufacture of a valve for a ball.
2. Background Art
Balls are provided with valves in order to inflate them after manufacture using a pump, in order to achieve a required pressure inside the ball. However, known balls and valves are not completely air tight so that the ball has to be inflated again and again over the course of time. This holds true in particular when the ball is subject to strong deformations during use, for example in the case of footballs or soccerballs.
Conventional valves for a ball consist of a casing and a core. The casing and the core are separately manufactured, usually from rubber or rubber mixtures. During assembly of the valve, the core is pressed into the casing by applying a considerable force.
Such a valve for a ball is described, for example, in DE 198 00 796 A1. The core of this valve is provided with an angular projection which has a rectangular shape in a cross section. The angular projection engages a groove of the casing so that the core is fixed in the casing. A similar construction is described in U.S. Pat. No. 5,915,407.
Further, U.S. Pat. No. 4,568,081 discloses a core in which a section with increased diameter has semicircular recesses which engage corresponding ribs on the casing.
DE 32 21 749 A1 describes a plug which seals the opening above a valve in order to improve air tightness and minimize leaking. The plug may comprise rounded projections. For inflating the ball, the plug can be taken out or pushed aside. However, the plug does not improve the air tightness of the valve itself.
U.S. Pat. No. 2,295,804 describes a two-part valve comprising a casing and a plug of such construction that the casing may be incorporated in the ball during its manufacture, and the plug thereafter inserted when inflation is desired.
The known valves for balls therefore have various disadvantages. Projections of the core indeed increase the surface of the core and may increase air tightness between the core and casing. On the other hand, it has been found that angular and rectangular projections and recesses of the core and the casing respectively make it easier for air to get out, for example due to deformations caused by strong forces acting on the ball.
Further, projections of the core cause deformations of the casing when the core is pressed into the casing during assembly of the valve. These deformations may damage the casing and reduce air tightness. In addition, the core may be damaged during insertion.
It is not just sufficient for a ball that is used during sports to have an airtight valve. Rather, the ball also has to have the proper pressure. Therefore, it should be possible to check the pressure in the ball in a simple way and to adjust it if necessary, even before its mobility and reactions are negatively affected. It is further known to provide a ball with a pressure sensor and to display the pressure.
For example, U.S. Pat. No. 4,577,865 describes a ball with a sensor for detecting an external force acting on the ball which has a display for a numerical value. U.S. Pat. No. 6,547,703 describes a training ball with a pressure sensor and a mechanical or electronic pressure display. Another pressure display for a ball is described in U.S. Pat. No. 5,755,634. Pressure sensors and displays are also known for tires and are described, for example, in U.S. Pat. No. 6,055,854 and U.S. Pat. No. 5,856,619.
The German patent application DE 10 2007 013 025 A1 discloses a ball with a pressure sensor wherein the measured pressure is displayed by a LED (light emission diode) which is attached to a transparent valve. Power supply shall be provided by an accumulator or a battery.
However, this document leaves open how the accumulator shall be provided with energy and how to realize this complex system inside the ball without impairing its smoothness of motion.
It is therefore the problem of the present invention to overcome the disadvantages of the prior art and to provide in particular a valve for a ball with improved air tightness and a method of manufacture of such a valve. A further problem of the invention is to provide a ball which not only has improved air tightness, but which also enables a user to check the air tightness reliably.